Peptoid nanosheets are a supramolecular assembly of a sequence-defined peptoid polymer. These peptoids have a repeating sequence pattern of ionic and hydrophobic monomers. This creates an amphiphilic polymer chain, which can stretch out and align with neighboring chains to create an extended planar assembly. Peptoid nanosheets are exciting because they can be easily synthesized and are tolerant to structural modification. They are a promising platform for building more complex nanostructures. We hope to engineer them to create materials that can mimic the molecular recogntion and catalytic properties of proteins, yet are much more stable.

"Block-28" peptoid is our prototypic nanosheet-forming peptoid. It is a 28mer, comprised of only 3 monomers: aromatic (Npe), anionic (Nce) and cationic (Nae). They are arranged in a two-fold perdiodic sequence pattern, alternating between a polar and a non-polar monomer. The charged groups are segregated into separate blocks, resulting in an amphiphilic structure with oppositely charged halves along the backbone. The alternating monomer pattern results in polar and non-polar groups on opposite sides of the molecule along its width. Both of these are critical to its ability to assemble into nanosheets. The Sigma strand backbone conformation enables adjacent sidechains to point in opposite directions.

Yellow = carbon, blue = nitrogen, red = oxygen.

Block-28 chemical structure: (Nae-Npe)7-(Nce-Npe)7

Block-28 spacefilling representation:

Nanosheet under the microscope:

Fluorescence microscopy

Atomic force microscopy (AFM)

Scanning electron microscopy (SEM)

Nanosheets can be stained with hydrophobic dyes like Nile Red,and can be readily imaged on a fluorecence microscope. The sheets are placed on a think slice of agarose gel, which serves to support the sheets in a single plane.

Nanosheets can be deposited on a mica and vlsualized by AFM. This provides a good measure of the nanosheet thickness, which is about 2.7 nm.

SEM reveals sharp edges and folds within the material.

Aberration-corrected
transmission electron microscopy

Free-floating nanosheets (32 sec)

Abberation-corrected TEM of a nanosheet supported on a holey carbon grid indicates alignment of chains running parallel to one another, separated by a distance of 4.5 Angstrom.

Nanosheets are free-floating in water and can be made in high yield. Here we pan over a large sample of nanosheets so you can get a sense of the uniformity/heterogeneity.

Computational modeling of nanosheets:

Bilayer Architecture: Molecular dynamics simulations provide an atomic-level view of the molecular structure. The peptoids in the nanosheet align parallel to one another in a brick-like pattern. Two layers face each other, such that the hydrophobic aromatic groups are buried in the center and the polar groups face outward toward solvent. Download the molecular srtucture of a section of a nanosheet with water molecules here (in a .pdb file format, viewable in PyMol): nanosheet.pdb (structure v6 from the Nature paper below)